signifi cantly diff ering microstructures (Fig. 3). T e elevated magnesium led to a signifi cant increase in the mea- sured and simulated nodularity in the steps of the step casting. T e same higher nodularities were shown in the rapidly solidifying areas of the engine block versus the thick-walled bearing segments. Generally, the measured and


3


predicted nodularities matched well within the measured range (Fig. 4). T e step casting and crankcase samples were used in numerous fatigue test runs. Using the mathematical methods of variance and regression analysis, the researchers developed a correlation between local micro- structure and durability using the


experimental data. Essential parts of the correlation function are the graphite shape and amount, as well as the pearlite fraction. No dominant microstructure parameter was found, so the correct combination of parame- ters is necessary to achieve the desired mechanical properties. T e accuracy of the model was determined to be 83%.


Results and Conclusions


T e essential mechani-


cal application loads of a crankcase are caused by


the pressures apparent during ignition. T ey are led through the pistons and connection rods into the crankshaft, bearings and bearing bridges, into the screws and fi nally into the crankcase. T e durability of an engine is


proven through extensive durability runs on engine test stands. Crankcase durability is evaluated on a simplifi ed two-axis impulse test stand (Fig. 5). T e two-axis impulse test derives


two inscribing force ellipses from the simulation results, which are scaled to


Fig. 5. Researches used a two-axis impulse test stand on the crankcase casting.


Fig. 6. Elongation profi les were compared to locally measured elongation signals to fi ne-tune the models. Jul/Aug 2013 | METAL CASTING DESIGN & PURCHASING | 45


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